package com.sjy.ylxt.utils;

import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;

/**
 * 描述: Twitter的分布式自增ID雪花算法snowflake
 **/
public class SnowFlakeUtil {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATA_CENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
//    private final static long MACHINE_LEFT = SEQUENCE_BIT;
//    private final static long DATACENTER_LEFT = MACHINE_LEFT + MACHINE_BIT;
//    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATA_CENTER_BIT;


    private final static long DATA_CENTER_LEFT = MACHINE_BIT;
    private final static long SEQUENCE_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
    private final static long TIMESTMP_LEFT = SEQUENCE_LEFT + SEQUENCE_BIT;

    private long datacenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    public SnowFlakeUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATA_CENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 获取实例
     *
     * @return
     */
    public static SnowFlakeUtil getInstance() {
        return getInstance(true);
    }

    public static SnowFlakeUtil getInstance(boolean random) {
        if (random) {
            Random rand = new Random();
            int min = 0;
            int max = 30;
            int s = rand.nextInt(max) % (max - min + 1) + min;
            int e = rand.nextInt(max) % (max - min + 1) + min;
            return getInstance(s, e);
        } else {
            return getInstance(1, 1);
        }
    }

    private static final ConcurrentHashMap<String, SnowFlakeUtil> SNOW_MAP = new ConcurrentHashMap<>();

    /**
     * 获取实例
     *
     * @param datacenterId
     * @param machineId
     * @return
     */
    public static SnowFlakeUtil getInstance(long datacenterId, long machineId) {
        String key = new StringBuilder().append("datacenterId=").append(datacenterId).append(" machineId=").append(machineId).toString();
        SNOW_MAP.putIfAbsent(key, new SnowFlakeUtil(datacenterId, machineId));
        return SNOW_MAP.get(key);
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

//        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
//                | datacenterId << DATACENTER_LEFT       //数据中心部分
//                | machineId << MACHINE_LEFT             //机器标识部分
//                | sequence;                             //序列号部分

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | sequence << SEQUENCE_LEFT             //序列部分
                | datacenterId << DATA_CENTER_LEFT      //数据中心部分
                | machineId;                            //机器部分
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }

}